1. Field of the Invention
The present invention relates to a device for the removal of air from flotation foam formed during flotation of a paper fiber containing suspension that includes a driven rotor.
2. Discussion of Background Information
The separation of air from flotation foam that accumulates during the flotation of fibrous material suspensions, e.g., in recovered paper processing, is necessary to be able to further process the flotation foam. As is known, flotation foam, which is formed during the flotation of a paper-fiber-containing suspension, is particularly hard to handle, since it is difficult to deaerate or dewater. Such a flotation foam is fluid and pumpable only to a limited extent, and tends to lodge on or adhere to the walls.
A device for the separation of air from flotation slurries is known, e.g., from German Patent No. 40 09 042 C2. This device essentially includes a hydrocyclone, which although it is well suited to the deaeration of liquids and foams, works as a hydraulic machine in the closed system, which requires a device with appropriate apparatus and presupposes at least a certain fluidity of the foam.
German Patent Application No. 35 19 374 A1 describes a mechanical foam breaker that can be plunged directly into the upper layer of foam. Such mechanical foam breakers can be used, e.g., in a foam collecting tank of a flotation unit. The foam breakers detect only the upper, strongly air-containing foam layer, draw this in and centrifuge the liquid portion away radially, whereby the drops of liquid assist secondarily in causing the surface foam bubbles to burst. Lower foam layers are not detected by this system. In the lower layers, a very heavy, wet foam is formed that is not subjected to a forced deaeration. The deaeration of this wet foam takes place only by sedimentation, which requires long dwell times. This device is relatively expensive in its design construction, the space required, and also with respect to its energy consumption.